In machines, such as copiers or printers, paper or other print-receiving material is held in a paper bin and fed, one sheet at a time, into the machine. Frequently, paper bins are used which hold a large amount of paper; for example, a stack of 500 sheets or more. To reload a bin, a paper tray is usually slideably removed from operating engagement within the machine, a stack of paper is placed onto the tray and the tray is returned to operating position within the machine. Normally, the stack of paper is placed on a tray which is mounted on powered elevator mechanisms which move the loaded tray upwardly so that the top sheet on the tray contacts paper feed rolls positioned above the paper stack. Arrangements of this kind, while suitable for more expensive high-volume machines, are not suitable for low cost slower speed desk-top machines. Usually, the low cost machines contain paper cassettes which may hold, for example, a stack of 25 or 50 sheets. In arrangements of this kind, the stack of paper is placed in the cassette on a tray which is spring biased upwardly so that the top sheet on the tray contacts paper feed rolls positioned above the cassette. In that manner, expensive powered elevator arrangements are avoided.
It is an object of this invention to provide a spring-biased tray capable of holding a large amount of paper (for example, 500 sheets or more) so that a paper bin of considerable size can be utilized on a low cost copier or printer.
It is another object of this invention to provide a spring mechanism for use with a paper tray which is easily adjustable for different weight and sizes of paper.
It is still another object of this invention to provide a paper tray with a leaf spring having an adjustable spring rate so that the contact force between the paper and the feed roll is maintained fairly constant as the number of sheets in the tray decreases from a large number, such as 500, to 0.
It is another object of this invention to provide a paper tray with a lift spring rate which is adjustable to provide a proper feed roll contact force regardless of the weight and size of the paper.
The objects of the instant invention have not been met in the prior art. U.S. Pat. No. 4,337,935 shows a typical paper cassette in which a coil spring lifts a paper tray so that contact may be made with a feed roll. Such a device is useful in paper cassettes, but is not capable of handling a large number of sheets.
U.S. Pat. No. 4,350,328 shows a sheet-feeding apparatus in which a pivotally disposed tray is urged upwardly by an arm which is pivotally mounted and biased by a coil spring.
U.S Pat. No. 4,765,604 shows a paper tray upwardly biased by an arm which is pulled upwardly by a coil spring.